Plankton communities in the northern Adriatic Sea: Patterns and changes over the last 30 years

In this work, we aim to describe the main features of the plankton communities analysed over 30 years of oceanographic cruises in the northern Adriatic Sea (NAS). We highlight the ecological complexity of the NAS by analysing the temporal variations of the abundance and species composition of the phytoplankton and mesozooplankton communities in different regions of the basin, which contain marked variations of abiotic and biotic parameters, both over time and space. A large interannual variability in the phytoplankton and mesozooplankton abundance was observed. For phytoplankton, the abundance exhibited an alternation of peaks and low values, primarily driven by the flooding or drought of the Po River. The mesozooplankton species composition changed significantly over past 20 years, primarily due to differences in the abundance of some of the copepod species. For both of the plankton communities, the results suggest that the phenological traits of the taxa, more than the spatial and temporal variations of the main abiotic parameters, drive the seasonal changes in the community composition.